Most mobile phones used in Europe, as well as many in the United States, run on the system called Groupe Speciale Mobile, or Global System for Mobile Communications (GSM). These phones require a SIM card in order to operate. This is in contrast to the Code Division Multiple Access (CDMA) system, which is common to mobile phones in the United States and do not use SIM cards.
Definition of SIM Cards
SIM is an acronym that stands for Subscriber Identity Module. SIM cards contain the subscriber information of the individual mobile phone user and identify the user to the network. SIM cards may also contain applications and personal data, such as stored telephone numbers. They are usually about the size of a thumbnail and are inserted into the mobile phone.
SIM Cards on Unlocked Mobile Phones
An unlocked phone is not operational without a SIM card. However, any GSM-compatible SIM card may be used with an unlocked phone. Personal data such as telephone numbers may be stored on the SIM card or on the phone itself. The operational data for the phone is stored on the SIM card.
SIM Cards on Locked Mobile Phones
A locked mobile phone will often be supplied to the customer with the SIM card already installed and programmed. While the SIM card can be physically removed from a locked mobile phone, the phone will not operate without it. It is not possible to substitute another SIM card into a locked phone unless it is unlocked by the carrier or by unlocking software.
SIM Cards Versus Re-Usable Identification Module (R-UIM) Cards
CDMA mobile phones do not use SIM cards. However, Re-Usable Identification Module (R-UIM) cards have been used in China since 2002. This technology works on a similar principle as SIM cards. As of 2009, development is underway to make R-UIM cards available in the United States, to make interchangeability for CDMA mobile phones possible.
Considerations for Travel
People who travel to many different destinations may have several SIM cards, which allow them to use a single unlocked mobile phone with their stored phone numbers and to obtain a local telephone number wherever they are.
Multiple-band GSM-network mobile phones can often be used overseas, whether locked or unlocked, although international roaming charges for locked mobile phones can be prohibitively high. Network bands for GSM phones are 850 and 1900, widely used in North and South America, and 900 and 1800, widely used in Europe. Tri-band mobile phones usually carry the 850, 1800 and 1900 bands, while quad-band mobile phones carry all four bands.
Tags: mobile phones, mobile phone, locked mobile, United States, CDMA mobile